1. Field of the Invention
The present invention relates to a balance-to-unbalance (balun), and more particularly, to a balun of which the whole size can be reduced.
2. Description of the Related Art
A balance-to-unbalance (balun) is a circuit converting an unbalanced signal into a balanced signal or a balanced signal into an unbalanced signal.
FIG. 1 is a perspective view of a related art balun, and FIG. 2 is a cross-sectional view taken along line I-I′ of FIG. 1. Referring to FIGS. 1 and 2, a related art balun 90 includes a base substrate 10, a ground electrode 20, first and second output lines 30 and 40, first and second conductors 50 and 60, an input line 70, and a dielectric layer 80.
In detail, the ground electrode 20 is provided on a lower surface of the base substrate 10, and the first and second output lines 30 and 40 and the input line 70 are provided on an upper surface of the base substrate 10. The ground electrode 20 covers the entire lower surface of the base substrate 10.
The first and second output lines 30 and 40 are spaced apart from each other and face each other based on a central line crossing the base substrate 10. The first and second output lines 30 and 40 are patterned into a substantially  configuration.
A first output port OP1 is provided at an end of the first output line 30 and outputs a first output signal corresponding to an input signal received from the input line 70. A second output port OP2 is provided at an end of the second output line 40 and outputs a second output signal corresponding to the input signal received from the input line 70. The first and second output ports OP1 and OP2 are adjacent to each other.
The first and second conductors 50 and 60 electrically connect the first and second output lines 30 and 40 to the ground electrode 20.
In other words, the first conductor 50 is interposed between the ground electrode 20 and the first output line 30. Here, a portion of the base substrate 10 is removed to form a first via hole, and the first conductor 50 is formed in the first via hole to electrically connect the ground electrode 20 to the first output line 30. As a result, the first output line 30 is electrically connected to the ground electrode 20.
The second conductor 60 is interposed between the ground electrode 20 and the second output line 40. Here, a portion of the base substrate 10 is removed to form a second via hole, and the second conductor 60 is formed in the second via hole to electrically connect the ground electrode 20 to the second output line 40. As a result, the second output line 40 is electrically connected to the ground electrode 20.
The input line 70 is provided above the first and second output lines 30 and 40. An input port IP is provided at an end of the input line 70 adjacent to the first output line 30 and receives an input signal from an external source.
A dielectric layer 80 is provided on an upper surface of the base substrate 10 on which the first and second output lines 30 and 40 are formed. The dielectric layer 80 is interposed between the first and second output lines 30 and 40 and the input line 70.
If an unbalanced signal is input to the input port IP, the unbalanced signal is input to the first and second output lines 30 and 40, and the first and second output ports OP1 and OP2 convert the unbalanced signal into a balanced signal to output first and second output signals, respectively. Here, the first and second output lines 30 and 40 respectively output the first and second output signals as two half signals into which the input signal is divided.
As described above, an input signal is divided into two half signals, the two half signals are output as first and second output signals, and a difference between phases of the first and second output signals is about 180°. For this purpose, a length of a portion of the input line 70 positioned above the first output line 30 must be about ¼ of an input wavelength λ, and a length of a portion of the input line 70 positioned above the second output line 40 must also be about ¼ of the input wavelength λ. Also, lengths of the first and second output lines 30 and 40 facing the input line 70 must each be about ¼ of the input wavelength λ.
As described above, the lengths of the first and second output lines 30 and 40 facing the input line 70 must each be about ¼ of the input wavelength λ so that the balun 90 receives the unbalanced signal and outputs the balance signal through the first and second output ports OP1 and OP2. As a result, there is a limitation to reducing a whole size of the balun 90.